* The New Puberty: How to navigate early development in today's girls.Just a generation ago, fewer than 5 percent of girls started puberty before the age of 8; today that percentage has more than doubled. Early puberty is not just a matter of physical transformation — it’s deeply psychological too, with effects that can put a girl at higher risk for behavioral problems as well as long-term health challenges such as obesity, depression, eating disorders, and even cancer. Buy.